This question tests 1st grade ability to determine the unknown whole number in an addition or subtraction equation (CCSS.1.OA.8). When the unknown is the starting number in addition (like in ? + b = c), we work backwards by subtracting the known addend from the result: c - b = ?. We can check by adding the found number back: ? + b should equal c. The equation is ___ + 3 = 10. Choice C is correct because subtracting 10 - 3 = 7, and we can verify: 7 + 3 = 10. Choice A is a common error where students add the given numbers instead of subtracting, like 10 + 3 = 13, which happens because working backwards is less intuitive and they may try the wrong operation. To help students: Teach each unknown position explicitly (result, addend, start); show how to check answer by substituting back into equation; for start unknown, explicitly teach 'work backwards' by subtracting known addend from result; use part-part-whole diagrams to visualize relationships; practice with concrete examples using objects; show related fact families (if 7 + 3 = 10, then 10 - 3 = 7); emphasize checking: substitute answer back into equation to verify it's true; provide many examples with unknowns in all positions.

This question tests 1st grade ability to determine the unknown whole number in an addition or subtraction equation (CCSS.1.OA.8). When the unknown is the minuend in subtraction (like in ? - b = c), we work backwards by adding the subtrahend to the result: c + b = ?. We can check by subtracting: ? - b should equal c. The equation is □ - 2 = 8. Choice A is correct because adding 8 + 2 = 10, and we can verify: 10 - 2 = 8. Choice D is a common error where students multiply or use a different operation, like 8 x 2 - something leading to 12, which happens because working backwards is less intuitive. To help students: Teach each unknown position explicitly (result, addend, start); show how to check answer by substituting back into equation; for minuend unknown, explicitly teach 'work backwards' by adding subtrahend to result; use part-part-whole diagrams to visualize relationships; practice with concrete examples using objects; show related fact families (if 10 - 2 = 8, then 8 + 2 = 10); emphasize checking: substitute answer back into equation to verify it's true; provide many examples with unknowns in all positions.

This question tests 1st grade ability to determine the unknown whole number in an addition or subtraction equation (CCSS.1.OA.8). When the unknown is the result in a subtraction equation (like in a - b = ?), we simply subtract the subtrahend from the minuend to find the difference. We can use counting back, objects, or number lines to compute it directly. The equation is 18 - 9 = ?. Choice C is correct because 18 - 9 = 9, so ? = 9. Choice D is a common error where students add the numbers instead of subtracting, getting 18 + 9 = 27; this happens because they may misread the operation or not recognize the need for subtraction. To help students: Teach each unknown position explicitly (result, subtrahend, minuend); show how to check answer by substituting back into equation; for result unknown in subtraction, it's direct computation; use part-part-whole diagrams to visualize relationships; practice with concrete examples using objects; show related fact families (if 18-9=9, then 9+9=18); emphasize checking: substitute answer back into equation to verify it's true.

This question tests 1st grade ability to determine the unknown whole number in an addition or subtraction equation (CCSS.1.OA.8). When the unknown is the minuend in subtraction (like in ? - b = c), we work backwards by adding the subtrahend to the result: c + b = ?. We can check by subtracting: ? - b should equal c. The equation is □ - 5 = 7. Choice B is correct because 7 + 5 = 12, and we can verify: 12 - 5 = 7. Choice A is a common error where students subtract instead of adding, getting 7 - 5 = 2; this happens because working backwards is less intuitive and they don't use the inverse operation. To help students: Teach each unknown position explicitly (result, subtrahend, minuend); show how to check answer by substituting back into equation; for minuend unknown, explicitly teach 'work backwards' by adding subtrahend to result; use part-part-whole diagrams to visualize relationships; practice with concrete examples using objects; show related fact families (if 12-5=7, then 7+5=12); emphasize checking: substitute answer back into equation to verify it's true.

This question tests 1st grade ability to determine the unknown whole number in an addition or subtraction equation (CCSS.1.OA.8). When the unknown is the starting number in addition (like in ? + 8 = 13), we work backwards by subtracting the known addend from the result: 13 - 8 = 5. We can check by adding: 5 + 8 = 13. The equation is □ + 8 = 13. Choice C is correct because subtracting 13 - 8 = 5, and we can verify: 5 + 8 = 13. Choice A is a common error where students add the numbers instead of subtracting, getting 8 + 13 = 21, not using the inverse operation. To help students: Explicitly teach 'work backwards' for start unknown; use part-part-whole models; practice substitution to verify; connect to fact families; use concrete examples with objects.

This question tests 1st grade ability to determine the unknown whole number in an addition or subtraction equation (CCSS.1.OA.8). When finding the result in addition (like in 3 + 9 = ?), we add the numbers: 3 + 9 = 12. Use counting or known facts. The equation is 3 + 9 = ?. Choice D is correct because 3 + 9 = 12, so ? = 12. Choice A is a common error like adding wrong (3 + 10 = 13), due to calculation mistake. To help students: Teach direct addition; use counters; practice checking; connect to fact families; provide many examples.

This question tests 1st grade ability to determine the unknown whole number in an addition or subtraction equation (CCSS.1.OA.8). When the unknown is an addend (like in 6 + ? = 10), we find what number added to 6 equals 10 by subtracting: 10 - 6 = 4. Counting on from 6 to 10 (7,8,9,10) gives 4 steps. The equation is 6 + ? = 10. Choice C is correct because 6 + 4 = 10, so ? = 4. Choice B is a common error where students add the numbers, getting 6 + 10 = 16, instead of subtracting. To help students: Connect addend unknown to subtraction (CCSS.1.OA.4); use diagrams and objects; teach checking by substitution; practice fact families; vary unknown positions.

This question tests 1st grade ability to determine the unknown whole number in an addition or subtraction equation (CCSS.1.OA.8). When the unknown is the subtrahend (like in 12 - ? = 7), we find what number subtracted from 12 gives 7, which can be done by subtracting: 12 - 7 = 5. We can also think of it as addition: what plus 7 equals 12, so 7 + 5 = 12. The equation is 12 - □ = 7. Choice B is correct because 12 - 5 = 7, so the unknown is 5. Choice A is a common error where students add instead, getting 12 + 7 = 19, not recognizing the need for inverse operations. To help students: Teach subtrahend unknown by connecting to addition; use fact families (12 - 5 = 7, 7 + 5 = 12); practice checking by substituting; use manipulatives; emphasize different unknown positions.

This question tests 1st grade ability to determine the unknown whole number in an addition or subtraction equation (CCSS.1.OA.8). When finding the result in a subtraction equation (like in 15 - 6 = ?), we simply compute the operation by subtracting the second number from the first. We can think of it as taking away 6 from 15, counting backwards or using manipulatives. The equation is 15 - 6 = ?. Choice B is correct because 15 - 6 = 9, so ? = 9. Choice A is a common error where students might add instead of subtracting, getting 15 + 6 = 21, but subtraction requires understanding removal. To help students: Teach result unknown in subtraction as direct computation; use objects to model taking away; practice with number lines; emphasize checking by adding back (9 + 6 = 15); provide varied examples.

This question tests 1st grade ability to determine the unknown whole number in an addition or subtraction equation (CCSS.1.OA.8). When the unknown is the subtrahend (like in 18 - ? = 10), we find what subtracted from 18 gives 10 by subtracting: 18 - 10 = 8. Or think as addition: 10 + 8 = 18. The equation is 18 - □ = 10. Choice B is correct because 18 - 8 = 10, so □ = 8. Choice A is a common error of adding, getting 18 + 10 = 28, not using inverse. To help students: Link to addition; use fact families; practice substitution; model with objects; teach unknown positions explicitly.